1. Field of the Invention
The present invention relates to suspension systems for ground level loading trailers and in particular to a torsion slide suspension apparatus for ground level loading trailers.
2. Description of the Prior Art
Ground level loading trailers, sometimes referred to as drop-bed trailers, mechanically lower the bed of a trailer to ground level to improve loading of machines, equipment and goods onto a trailer. These types of trailers are popular because one person can lower the trailer bed to load and unload cargo safely without having to disconnect the trailer from the tow vehicle and without requiring a ramp. With a ground level loading trailer, there are no winches, pulleys or ramps to deal with. Often, these trailers are used by persons who desire to drive their machine or vehicle onto the trailer. Thus, these trailers need to be capable of handling a fairly significant load mass.
Unfortunately, one of the drawbacks of ground level loading trailers is the lack of structural support provided by the frame and chassis. This weakness reflects the need to design the frame and suspension so that the trailer bed can lower to the ground between the wheels, which means most designs eliminate some conventional cross-supports and the wheel axle. Thus, a need exists to provide a strong suspension system for ground level loading trailers that can support hauling heavy equipment.
Attempts to provide a ground level loading trailer without disadvantages has proved elusive. For examiner, U.S. Pat. No. 8,191,922 provides a modern drop-bed trailer with a guide mechanism that includes a cable system with cable tension device and a pulley block. While the guide mechanism used permits adjustment of the trailer bed height on unlevel surfaces, the design adds complexity and likely adds to the cost of manufacture. Another prior art trailer includes independently pivotal wheel carrying support arms connected to a trailer frame by a half leaf spring, wherein each support arm is pivotal by a respective cable winch. Another common type of ground level loading trailer uses a U-shaped axle and a frame mounted by leaf springs to the axle. The leaf springs on this commons type of trailer wear because of the increased torsion caused by the U-shaped frame, as the wheels are supported by the leaf springs rather than a transverse axle. The wear on the leaf springs cause premature tire wear. A modification of this type of trailer provides an air suspension system instead of leaf springs. However, the air suspension system is high maintenance and requires expensive components.
Thus a need exists to provide a ground loading trailer with an improved suspension system that decreases tire wear and cost of manufacture.